The invention relates to a method of drying hair by supplying hot air, using remote sensing of the moisture content of the hair.
The invention also relates to a hair dryer including means for supplying a stream of hot air for drying moist hair and means for the remote sensing of the moisture content of the hair.
Such a method and hair dryer are known from Patentschrift DE 34 33 246. During hair drying there is always a risk that the hair is made too dry by the hot air from the hair dryer, as a result of which the hair is liable to be damaged. The temperature increases rapidly where the hair has dried, which is detrimental to the hair and painful for the scalp. For a satisfactory and comfortable result it is therefore important to know how much moisture is left in the hair and to take steps if the moisture content decreases below a given limit. In the known hair dryer the moisture content is measured by means of a moisture sensor disposed in the circulating air stream in a hair-drying hood. The measurement of the moisture content of the hair is then measured remote from the hair but is limited to hair-drying hoods in which the hot air circulates. However, this known method of moisture measurement cannot be used in the case of hand-held hair-dryers because in these dryers no hot air circulates within an enclosed space.
Furthermore, hair dryers are known, for example from International Application WO 97/09898, which have electrodes arranged on an accessory which comes into contact with the hair during drying. By means of the electrodes the moistness of the hair is measured on the basis of the resistance or capacitance of the hair between the electrodes. However, in this type of dryer the measurement of the moistness of the hair is not effected at a distance and has therefore only a limited field of use.
From the Demande de brevet europeen EP 0 679 350 a hair dryer is known in which the temperature of the hair to be dried is measured in a contactless manner, at a distance from the hair, by means of an infrared sensor arranged on the housing of the hair dryer. The temperature of the hair is then determined on the basis of the infrared radiation emitted by the hair. However, the temperature of the hair is only an indirect indication of the moisture content of the hair and is consequently less reliable.